The invention relates to a continuously operating drier for webs or sheets of a workpiece in. The inventive drier provides different stages of treatment. The workpiece follows a course between endless belts which pass over guide rollers.
A continuously operating drier of the above-mentioned category has been proposed. The drier is particularly intended for veneer--like plywood--and has a three-belt drying chamber and a thereto connected cooler downstream thereof. The conveyor belts lie under pressure against the veneer and cover the veneer in such a way that the drying heat is essentially transmitted by way of the conveyor belts. Moreover, a glazed or smoothed appearance is bestowed on the veneer by means of the conveyor belt.
Veneer is in the form of a thin layer of generally uniform thickness and is generally cut from timber of fine appearance. The veneer is then glued to the surface of a less expensive material. Since the drying of the veneer takes place exclusively in the three-belt drier according to the above proposal, breakage and cracking of the surface of the veneer can occur as the belts turn the veneer over around guide rollers to thereby expose both longitudinally and sides of the veneer to heat in the drier. The result is diminished value--especially when the veneer is ornamental or is finely grained wood. Another disadvantage of this conventional proposal is that separate regulation of the climate and temperature is not possible for the different stages of the drying progress.
This risk of breakage or cracking can be overcome by using a single-belt drier. However, this advantage is accompanied by the disadvantages of a correspondingly longer length of the drier.
Another proposed continuous drier involves an assembly having a sequence of drying stages adjusted in accordance with a desirable heating or drying capacity. These stages are each provided with separate temperature controls. The drier is provided with equidistantly spaced suction means arranged above and/or below the pathway for the workpiece. However, the veneer workpiece is not satisfactorily dried because the suction means block the heat from portions of the workpiece. Consequently, the desired glazed or smoothed effect does not occur.